Medical institutions are equipped with a radiographic apparatus configured to emit radiation to image a subject. Such a radiographic apparatus conducts fluoroscopy to the subject while emitting weak radiation to the subject and thereafter emitting strong radiation to the subject, thereby imaging the subject. See, for example, Japanese Patent Publication No. 2000-261724A and H09-271023A.
In the fluoroscopy of the subject, weak radiation is repeatedly emitted, whereby an animated image (animated image) containing a fluoroscopic image of the subject is obtained. Accurate diagnosis cannot be conducted with the animated image (animated image) obtained in the above manner. An operator controls a position of the subject while observing the animated image such that a region of interest of the subject is located within a field of view of the radiographic apparatus.
Upon completing the control in position of the subject, the operator stops obtaining the animated image. Thereafter, the operator issues a command to the radiographic apparatus to conduct radiography to the subject so as not to move the subject in this condition. Then, the radiographic apparatus irradiates the subject with strong pulsed radiation, thereby taking an image (static image) containing a fluoroscopic image of the subject. The taken image contains a clear fluoroscopic image of the subject. Then, the operator conducts various diagnoses in accordance with the image.
The following describes a conventional method in detail. Upon starting fluoroscopy to a subject, the radiographic apparatus firstly acquires brightness of the fluoroscopic image of the subject appearing in the animated image. Thereafter, the radiographic apparatus performs feedback control to radiation irradiation control such that the brightness becomes appropriate brightness. Consequently, if the animated image contains a dark fluoroscopic image of the subject due to the too thick subject, the fluoroscopy is continuously conducted while intensity of radiation gradually increases with the feedback control.
In this manner, the conventionally apparatus automatically controls the intensity of radiation while the fluoroscopy is continuously conducted. Immediately before completing the fluoroscopy, the animated image contains the fluoroscopic image of the subject with the brightness appropriate to visual recognition. Under this state, the fluoroscopy is completed.
After the fluoroscopy, radiography is performed to the subject. For the radiography, it is necessary to determine a control condition (radiography condition) of a radiation source in advance. This is because a suitable radiography condition varies depending on a frame of the subject, and thus is not uniform.
As a result, the conventionally apparatus determines the radiography condition from a feature that the feedback control is performed to irradiation by the radiation source during the fluoroscopy. That is, the radiography condition is obtained in accordance with radiation intensity immediately before completion of the fluoroscopy. As in the above embodiment, when the subject is too thick, the fluoroscopy is performed with higher intensity of radiation. Then radiography is performed with increased intensity of radiation accordingly, achieving a suitable radiography condition.
In this manner, the conventionally apparatus performs feedback control to the fluoroscopy condition depending on a thickness of the subject, and determines the radiography condition for taking an image in accordance with the controlled fluoroscopy condition. For concrete setting of the radiography condition, a thickness of the subject is estimated in accordance with radiation intensity immediately before completion of the fluoroscopy. Thereafter, radiation intensity upon radiography is set in accordance with the estimated body thickness.